Mg-based hydrides are one of the most promising hydrogen storage materials because of their relatively high storage capacity, abundance, and low cost. However, slow kinetics and stable thermodynamics hinder their practical application. In contrast to the substantial progress in the enhancement of the hydrogenation/dehydrogenation kinetics, thermodynamic tuning is still a great challenge for Mg-based alloys. At present, the main strategies to alter the thermodynamics of Mg/MgH₂ are alloying, nanostructuring, and changing the reaction pathway. Using these approaches, thermodynamic tuning has been achieved to some extent, but it is still far from that required for practical application. In this article, we summarize the advantages and disadvantages of these strategies. Based on the current progress, finding reversible systems with high hydrogen capacity and effectively tailored reaction enthalpy offers a promising route for tuning the thermodynamics of Mg-based hydrogen storage alloys.

Due to its relatively low cost, high hydrogen yield, and environmentally friendly hydrolysis byproducts, magnesium hydride (MgH₂) appears to be an attractive candidate for hydrogen generation. However, the hydrolysis reaction of MgH₂ is rapidly inhibited by the formation of a magnesium hydroxide passivation layer. To improve the hydrolysis properties of MgH₂-based hydrides we investigated three different approaches: ball milling, synthesis of MgH₂-based composites, and tuning of the solution composition. We demonstrate that the formation of a composite system, such as the MgH₂/LaH₃ composite, through ball milling and in situ synthesis, can improve the hydrolysis properties of MgH₂ in pure water. Furthermore, the addition of Ni to the MgH₂/LaH₃ composite resulted in the synthesis of LaH₃/MgH₂/Ni composites. The LaH₃/MgH₂/Ni composites exhibited a higher hydrolysis rate—120 mL/(g·min) of H₂ in the first 5 min—than the MgH₂/LaH₃ composite— 95 mL/(g·min)—without the formation of the magnesium hydroxide passivation layer. Moreover, the yield rate was controlled by manipulation of the particle size via ball milling. The hydrolysis of MgH₂ was also improved by optimizing the solution. The MgH₂ produced 1711.2 mL/g of H₂ in 10 min at 298 K in the 27.1% ammonium chloride solution, and the hydrolytic conversion rate reached the value of 99.5%.